This invention relates to an austenitic iron base alloy, and in particular to such an alloy useful for making valve seat inserts used in internal combustion engines, with the novel combination of good wear and corrosion resistance under actual use conditions.
Modified M2 tool steel and Silichrome XB represent two common groups of casting iron base alloys used for diesel engine intake valve seat inserts. In broad ranges, modified M2 tool steel comprises 1.2-1.5 wt % carbon, 0.3-0.5 wt % silicon, 0.3-0.6 wt % manganese, 6.0-7.0 wt % molybdenum, 3.5-4.3 wt % chromium, 5.0-6.0 wt % tungsten, up to 1.0 wt % nickel, and the balance being iron. U.S. Pat. No. 5,674,449 discloses a high speed steel-type iron base alloy with excellent wear resistance as exhaust valve seat inserts.
Modified Silichrome XB contains 1.3-1.8 wt % carbon, 1.9-2.6 wt % silicon, 0.2-0.6 wt % manganese, 19.0-21.0 wt % chromium, 1.0-1.6 wt % nickel, and the balance being iron. Another high carbon and high chromium-type iron base alloy for intake valve seat inserts contains 1.8-2.3 wt % carbon, 1.8-2.1 wt % silicon, 0.2-0.6 wt % manganese, 2.0-2.5 wt % molybdenum, 33.0-35.0 wt % chromium, up to 1.0 wt % nickel, and the balance being substantially iron. There are also several high chromium-type iron base alloys available for making intake valve seat inserts.
High carbon and high chromium-type nickel base alloys, such as Eatonite 2, have excellent corrosion resistance and also good wear resistance as exhaust valve seat inserts. However, these nickel base alloys normally do not exhibit good wear resistance as intake valve seat inserts due to the lack of combustion deposits and oxides to reduce metal-to-metal wear. Eatonite is a trade name of Eaton Corporation. Eatonite 2 is a common nickel base alloy for exhaust valve seat inserts, which contains 2.0-2.8 wt % carbon, up to 1.0 wt % silicon, 27.0-31.0 wt % chromium, 14.0-16.0 wt % tungsten, up to 8.0 wt % iron, and the balance being essentially nickel. There are several nickel base alloys with added iron and/or cobalt for valve seat inserts. U.S. Pat. No. 6,200,688 discloses a high silicon and high iron-type nickel base alloy used as material for valve seat inserts.
Stellite® 3 and Tribaloy® T4001 are two cobalt base alloys used as valve seat inserts for severe applications. U.S. Pat. Nos. 3,257,178 and 3,410,732 discuss such alloys. Tribaloy® T400 contains 2.0-2.6 wt % silicon, 7.5-8.5 wt % chromium, 26.5-29.5 wt % molybdenum, up to 0.08 wt % carbon, up to 1.50 wt % nickel, up to 1.5 wt % iron, and the balance being essentially cobalt. Stellite® 3 contains 2.3-2.7 wt % carbon, 11.0-14.0 wt % tungsten, 29.0-32.0 wt % chromium, up to 3.0 wt % nickel, up to 3.0 wt % iron, and the balance being cobalt. Stellite® and cobalt base Tribaloy® alloys offer both excellent corrosion and wear resistance. Unfortunately, these alloys are very expensive due to the high cost of the cobalt element.
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There are many powder metallurgy (PM) alloys available for making valve seat inserts. Here are a few examples in the PM alloys. Japanese Patent Publication No. 55-145,156 discloses an abrasion resistant sintered alloy for use in internal combustion engines which comprises 0.5 to 4.0 wt % carbon, 5.0 to 30.0 wt % chromium, 1.5 to 16.0 wt % niobium, 0.1 to 4.0 wt % molybdenum, 0.1 10.0 wt % nickel and 0.1 to 5.0 wt % phosphorus. Japanese Patent Publication No. 57-203,753 discloses an abrasion resistant sintered alloy containing 0.5-5 wt % carbon, 2-40 wt % of one or more of Cr, W, V, Nb, Ti, and B. Such a sintered alloy is melt-stuck by a means such as plasma, laser, or electron beam on a base material consisting of steel or cast iron. Japanese Patent Publication No. 60-258,449 discloses a sintered alloy for valve seat inserts. The alloy comprises 0.2-0.5 wt % carbon, 3-10 wt % molybdenum, 3-15 wt % cobalt, 3-15 wt % nickel, and the balance being iron.
Certain internal combustion engine valve alloys or valve facing alloys may also be classified into the same group of materials. U.S. Pat. No. 4,122,817 discloses an austenitic iron base alloy with good wear resistance, PbO corrosion and oxidation resistance. The alloy contains 1.4-2.0 wt % carbon, 4.0-6.0 wt % molybdenum, 0.1 to 1.0 wt % silicon, 8-13 wt % nickel, 20-26 wt % chromium, 0-3.0 wt % manganese, with the balance being iron. U.S. Pat. No.4,929,419 discloses a heat, corrosion and wear resistant austenitic steel for internal combustion exhaust valves, which contains 0.35-1.5 wt % carbon, 3.0-10.0 wt % manganese, 18-28 wt % chromium, 3.0-10.0 wt % nickel, up to 2.0 wt % silicon, up to 0.1 wt % phosphorus, up to 0.05 wt % sulfur, up to 10.0 wt % molybdenum, up to 4.0 wt % vanadium, up to 8.0 wt % tungsten, up to 1.0 wt % niobium, up to 0.03 wt % boron, and the balance being essentially iron.
There are some corrosion resistant alloys that also relate to present invention. U.S. Pat. No. 4,021,205 discloses a heat and abrasion resistant sintered powdered ferrous alloy, containing 1 wt % to 4 wt % carbon, 10 to 30 wt % chromium, 2 to 15 wt % nickel, 10 to 30 wt % molybdenum, 20 to 40 wt % cobalt, 1 to 5 wt % niobium, and the balance iron. U.S. Pat. No. 4,363,660 discloses an iron base alloy having high erosion resistance to molten zinc attack consisting of 0.01-2 wt % carbon, 0.01 to 2 wt % silicon, 0.01-2 wt % manganese, 1-6 wt % niobium or tantalum, 1-10 wt % molybdenum or tungsten, 10-30 wt % nickel, 10-30 wt % cobalt, 10-25 wt % chromium, and a balance of iron and inevitable impurities. U.S. Pat. No. 5,194,221 discloses hot gas resistant alloys containing 0.85-1.4 wt % carbon, 0.2-2.5 wt % silicon, 0.2-4 wt % manganese, 23.5-35 wt % chromium, 0.2-1.8 wt % molybdenum, 7.5-18 wt % nickel, up to 1.5 wt % cobalt, 0.2-1.6 wt % tungsten, 0.1-1.6 wt % niobium, up to 0.6 wt % titanium, up to 0.4 wt % zirconium, up to 0.1 wt % boron, up to 0.7 wt % nitrogen, and iron being the balance.
Continuous efforts to improve the performance, durability, and emission of internal combustion engines have resulted in a demand for valve seat insert materials which can withstand the corrosive and high stress conditions of such engines. Internal combustion engines for marine applications or equipped with exhaust gas recirculation (EGR) systems not only require intake valve seat insert materials with excellent wear resistance, but also good corrosion resistance to resist the acid environment formed due to introduction of exhaust gas into the intake system. However, it is difficult for current casting iron base valve seat insert alloys to possess both good wear and corrosion resistance. Therefore, it is the objective of this invention to develop an iron base alloy with both good corrosion and wear resistance to meet such requirements.